Viewing: dump valves?????????????????

**jasio1978** · 05-07-2010, 10:06 PM

Man, i love this site. as i said i have a good knowledge, i dont know it all by any means, and you lot are helping my knowledge grow.

it all makes sense to me tho..

**petescustompipes** · 21-07-2010, 12:44 PM

whats scavenging?

***HDi fun*** · 21-07-2010, 08:43 PM

Quote:

Originally Posted by petescustompipes

whats scavenging?

Scavenging is using the escaping exhaust gases velocity to create a slight vacuum in the combustion chamber/cylinder so that it helps to draw in a better intake charge of air and for that charge to arrive faster. Or more accurately, for the intake gas velocity to be higher. Thus increasing turbulence which in turn helps air/fuel mixing and ignition.

It's for this reason that the exhaust and intake valve open periods overlap between the exhaust and intake phases.

**Turboshaft** · 24-07-2010, 10:34 PM

it also helps trapped exhaust gasses in the cylinder mix with the air/fuel mixture

***HDi fun*** · 25-07-2010, 12:18 AM

Quote:

Originally Posted by Turboshaft

it also helps trapped exhaust gasses in the cylinder mix with the air/fuel mixture

That's pointless - exhaust gases need to go south, whether via a turbine or not. You don't want them remaining in the combustion chambers.

Diesel engines do not have throttles - there's nothing to dump.

**Turboshaft** · 31-07-2010, 12:15 AM

Quote:

Originally Posted by HDi fun

That's pointless - exhaust gases need to go south, whether via a turbine or not. You don't want them remaining in the combustion chambers.

Diesel engines do not have throttles - there's nothing to dump.

there will always be a small quantity of exhaust gases in the cylinder that won't flush no matter how you tune your exhaust manifold/ports and the best you can do is to make sure that they mix properly with the air/fuel otherwise you won't get a good combustion.

***HDi fun*** · 31-07-2010, 10:29 AM

Quote:

Originally Posted by Turboshaft

there will always be a small quantity of exhaust gases in the cylinder that won't flush no matter how you tune your exhaust manifold/ports and the best you can do is to make sure that they mix properly with the air/fuel otherwise you won't get a good combustion.

I know that. But what has it got to do with dump valves?

**jarrus** · 31-07-2010, 11:22 AM

I was thinking that as well,

but the only reason I would fit a dump valve on a diesel is to stop the wastegate flutter which really isn't healthy for a turbo, and some owners on turbo diesels report that the excess pressure reverses though the air filter, not good as well, I think this is due to the fact the the engines demand for air has decreased, I know technically that diesels always run lean unless you've got the hammer down but if you shove too much air in the engine will stall, same applies on a diesel engine if you add too much nitrous oxide, it just stalls and you can just start it up again,

i'd just use one to protect my turbo if i was running some "unholy" boost because all the extra has to be consumed by the engine as there is no throttle but it doesn't need it, hense a dump valve might have some purpose on a turbo diesel, I just got to make sure that if i have one it doesn't scare old people....

***HDi fun*** · 31-07-2010, 12:23 PM

I'm not aware of any engine makers who fit DVs to diesels. That's because there is no throttle and therefore nothing to dump.

Air goes into engine, gets compressed, expands again and then goes out the exhaust side.

Tell me this: What would trigger the DV?

**jarrus** · 31-07-2010, 07:08 PM

No one does, that's my point, you have to tap into the brake vacuum line and use a solenoid and a switch on the fuel pump arm or tap into the drive by wire throttle pedal and when you let off the pedal it dumps the pressure

***HDi fun*** · 31-07-2010, 08:20 PM

And if you did trigger it what's it going to dump?

Sorry but I cannot see the purpose of this with a diesel engine which breathes freely regardless of pedal position.

**jasio1978** · 02-08-2010, 10:58 PM

So. From what your saying is i dont need a dv. Cool, i wont waste the rhino.
Back to scavenging. I was always under the immpression that the idea of valve overlap, was more geared towards getting the exhaust out of the pot, then getting extra fuel air mix in.
Would it not be the same amount of mix going in, just that it was combusting better, due to no co, which dosnt burn.

**Turboshaft** · 02-08-2010, 11:16 PM

Quote:

Originally Posted by jasio1978

Would it not be the same amount of mix going in, just that it was combusting better, due to no co, which dosnt burn.

That's exactly my point , i didn't state that there will be extra air/fuel in, I was trying to explain that the overlap also causes a swirl which helps the residual co mix with the air/fuel and combust better.

To reiterate, the overlap forces the exhaust gas out, but a small fraction of it goes back into the pot (because of resonance/pulse effects i was told) and gets mixed into the air/fuel mixture. The better they mix , the better they burn.

Sorry again for not making myself clear , English is not my native language.

***HDi fun*** · 02-08-2010, 11:25 PM

Quote:

Originally Posted by jasio1978

So. From what your saying is i dont need a dv. Cool, i wont waste the rhino.
Back to scavenging. I was always under the immpression that the idea of valve overlap, was more geared towards getting the exhaust out of the pot, then getting extra fuel air mix in.
Would it not be the same amount of mix going in, just that it was combusting better, due to no co, which dosnt burn.

You don't need a DV. Valve overlap is the norm, scavenging is totally normal with four stroke engines. It's simply a matter of the degree as to how much overlap is designed in.

VVT systems adjust the valve timing in real time simply to make the best of what is ultimately a compromise.

As of yet the automotive industry hasn't designed and built the ideal internal combustion engine,